No detection technology "sees everything". Each family has a relevance domain, and the right practice is to pick the minimal mix that covers your real threats — not the maximum stack.
Passive radio-frequency detection (RF)
Principle: continuously listen to the bands used by drones (Wi-Fi 2.4 / 5.1 / 5.8 GHz, Bluetooth Legacy and Long Range) and the Remote ID frames. Detection is cooperative when the drone broadcasts its identity (Remote ID, French signalement) and non-cooperative when a drone is identified from its radio signature alone.
Strengths: very low installation cost, no emission so no transmit authorisation required, reliable identification of compliant consumer drones, easy VMS integration. Limits: an RF-silent home-made drone, or one flying fully autonomous without a radio link, remains invisible.
This is the DECTYR RX-5 approach: 5 km free-field range, multi-band coverage, multi-standard Remote ID (EN 4709-002, ASTM F3411-22a, JANS 0401, B-RID, French signalement).
Radar detection
Principle: emit a wave and analyse the return. Micro-Doppler small-drone radars exploit the propeller Doppler modulations to discriminate a drone from a bird.
Strengths: sees non-cooperative drones, all-weather, independent from RF signature. Limits: high cost, transmit licensing (ANFR, FCC), sensitivity to urban clutter, false-positive rate in complex environments.
Electro-optical detection (cameras + IR)
Principle: visible or thermal IR video analysed by detection / tracking algorithms. Mostly useful for verification ("is it really a drone?") and documentation, after another sensor triggered the alert.
Strengths: visual evidence, native VMS integration. Limits: narrow field of view, weather-sensitive, weak as a stand-alone initial detector.
Acoustic detection
Principle: capture the propeller signature via a mic array and recognise it spectrally.
Strengths: inexpensive, passive. Limits: short range (a few hundred metres), unusable in noisy environments (highways, cities). More of a complement than a primary sensor.
Quick decision matrix
- Cover Remote ID-compliant drones (90% of civil overflights): passive RF is enough.
- Cover non-cooperative drones in open fields: passive RF + radar.
- Dense urban overflights: passive RF + EO/IR for verification.
- Court-ready documentation: passive RF with signed PDF report + VMS clip.
- Critical infrastructure / defence: multi-sensor architecture RF + radar + EO/IR orchestrated by hypervision.
FAQ
Is passive RF detection enough?
For most civilian sites, yes — because most overflights are flown with consumer drones broadcasting Remote ID. For sites particularly exposed to modified or home-made drones, adding radar remains relevant.
Does rain or snow degrade detection?
Passive RF is very weakly impacted by weather. Radar shows little degradation. EO/IR suffers significantly from rain, fog and night (except thermal IR).
Can multiple RF detectors be combined?
Yes. Several DECTYR RX-5 units can cover a large site, with consolidated detections in DECTYR Hub.